Synthesis, structure, and reactivity of {(2-phosphinoethyl)silyl}-rhodium(I) complexes Rh[(κ2Si,P)-Me2Si(CH2)2PPh 2](PMe3)n (n = 2, 3)

Article abstract of DOI:10.1039/b201208c

A (2-phosphinoethyl)silylrhodium(III) complex RhH(Cl)[(κ²Si,P)-Me₂Si(CH₂) ₂PPh₂](PMe₃)₂ (1) was synthesized by the thermal reaction of RhCl(PMe₃)_n (n = 3, 4

Full text of DOI:10.1039/b201208c

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Synthesis, structure, and reactivity of {(2-phosphinoethyl)silyl}-
rhodium(I) complexes Rh[(ꢀ2Si,P)-Me2Si(CH2)2PPh2](PMe3)n
(n ؍ 2, 3)
Masaaki Okazaki,* Shin Ohshitanai, Hiromi Tobita* and Hiroshi Ogino
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578,
Japan
Received 1st February 2002, Accepted 19th February 2002
First published as an Advance Article on the web 5th April 2002
A (2-phosphinoethyl)silylrhodium() complex RhH(Cl)[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (1) was synthesized by
the thermal reaction of RhCl(PMe3)n (n = 3, 4) with HMe2Si(CH)2PPh2 at 50 ЊC for 2 h. Treatment of 1 with MeLi
gave a coordinatively unsaturated rhodium() complex Rh[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (2) which was possibly
produced via transient formation of RhH(Me)[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 and subsequent reductive
elimination of methane. X-Ray crystal structure analysis revealed that 2 adopts a slightly distorted square planar
geometry. When the reaction of 1 with MeLi was carried out in the presence of PMe3, a coordinatively saturated
silylrhodium() complex Rh[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)3 (3) was formed. According to the X-ray crystal
structure analysis, 3 adopts a five-coordinate, slightly distorted trigonal-bipyramidal arrangement in which the silyl
silicon atom and a PMe3 ligand occupy the axial positions. Variable temperature NMR measurements revealed that
both 2 and 3 undergo the exchange of PMe3 ligands on the NMR timescale. The exchange in 2 is intramolecular,
while that in 3 is intermolecular. Treatment of HSiMe2Ph with 2 gave rise to selective dehydrogenative coupling
of hydrosilanes to afford (SiMe2Ph)2 and RhH2[(κ2Si,P)-Me2SiCH2CH2PPh2](PMe3)2 (5).
employed.6 We report here the synthesis, crystal structure, and
Introduction
properties of coordinatively unsaturated and saturated Rh()
Wilkinson-type complexes RhCl(PR3)3 have been employed as
silyl complexes Rh[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)n (n = 2,
active homogeneous catalysts for various transformation reac-
3). Reactions of these Rh() silyl complexes with monohydro-
tions of organic compounds.1 Introduction of silyl ligands in
silane were also examined. A part of this work has been
place of chlorine ligands could enhance or change the reactivity
published as a preliminary communication.7
and catalytic performance of transition metal complexes,
because silyl ligands exhibit an exceptionally strong σ-donor
character and high trans-influencing ability.2 Although silyl-
rhodium() complexes are somewhat rare, a few compounds of
the type LnRhSiR3 (L = tertiary phosphine) have been syn-
thesized.3,4,5,6,7 The first structurally characterized silylrho-
dium() complex has been reported by Stobart.3 Treatment of
Rh(tripsi)H(Cl) with MeLi under a CO atmosphere gave
Rh(tripsi)(CO) via reductive elimination of methane (tripsi =
Si(CH2CH2PPh2)3). Milstein et al. reported the activation
of carbon–fluorine bonds by the coordinatively unsaturated
rhodium() complex L3RhSiR3 (L = PMe3, R3 = Me2Ph, Ph3):4
the Rh() silyl complex reacts quantitatively with C6F6 at room
temperature to give L3RhC6F5 and R3SiF. This experimental
result indicates that Rh() silyl complexes are potentially appli-
cable to active catalysts. However, facile elimination of silyl
ligands from the metal center has retarded the progress of such
application. Thorn and Harlow reported studies on the react-
ivity of L3RhSiPh3 (L = PMe3).5 When the solution of the
Rh() silyl complex is exposed to ethylene, carbon–silicon bond
Results and discussion
Synthesis of RhCl(H)[(ꢀ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (1)
The rhodium() complex RhCl(H)[(κ2Si,P)-Me2Si(CH2)2-
PPh2](PMe3)2 (1) can be readily prepared by the thermal reac-
tion shown in eqn. 1. Workup and recrystallization from
(1)
toluene–hexane at Ϫ10 ЊC afforded ivory crystals in 90% yield.
1
The H, 13C, 29Si, and 31P NMR spectral data established that
1 possesses chloro, hydrido, and silyl ligands in a mer-relation-
1
ship. The H resonance of Rh–H appears at Ϫ9.32 ppm as
double quartets by coupling with one trans-31P nucleus (2J(PH)
= 158 Hz) and one 103Rh (1J(RhH) = 15 Hz) and two cis-31P
nuclei (2J(PH) = 15 Hz). The coupling pattern of the 31P reson-
ances indicates that three phosphorus atoms are located in a
mer-relationship. In the 29Si{1H} NMR spectrum, the signal
appears at 40.4 ppm as a dddd by coupling with 103Rh (1J(RhSi)
= 26.1 Hz) and three cis-31P nuclei (2J(PSi) = 10.5, 8.2, 6.9 Hz).
The ORTEP drawing of 1 is shown in Fig. 1. Selected bond
distances and angles are listed in Table 1. The complex adopts a
six-coordinate, slightly distorted octahedral arrangement in
which three phosphorus atoms are located in a mer-relationship
formation occurs readily to give (CH ᎐CH)SiPh and unidenti-
᎐
2
3
fied product(s) containing rhodium. This reaction may proceed
via olefin insertion into a rhodium–silicon bond and subsequent
β-hydrogen elimination. The Rh() silyl complex also reacted
with excess methyl iodide to form MeSiPh3 and mer-L3I2-
RhCH3. A plausible formation mechanism of these products
involves the transient formation of the Rh() iodo(methyl)-
(silyl) complex L3RhI(CH3)(SiPh3). Subsequently, reductive
elimination of MeSiPh3 and oxidative addition of MeI occur to
give the final products. To suppress such elimination of silyl
ligands, chelate-type (2-phosphinoethyl)silyl ligands have been
DOI: 10.1039/b201208c
J. Chem. Soc., Dalton Trans., 2002, 2061–2068
This journal is © The Royal Society of Chemistry 2002
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Table 1 Selected bond distances (Å) and angles (Њ) for RhCl(H)-
[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (1)
Table 2 Selected bond distances (Å) and angles (Њ) for Rh[(κ2Si,P)-
Me2Si(CH2)2PPh2](PMe3)2 (2)
Rh–Cl
Rh–P2
Rh–Si
P1–C2
P1–C11
P2–C18
P3–C20
P3–C22
Si–C3
2.535(1)
2.306(1)
2.331(1)
1.823(4)
1.837(4)
1.827(5)
1.822(4)
1.822(4)
1.888(5)
1.542(6)
Rh–P1
Rh–P3
Rh–H
P1–C5
P2–C17
P2–C19
P3–C21
Si–C1
2.2925(9)
2.366(1)
1.71(8)
1.822(4)
1.814(5)
1.818(5)
1.815(4)
1.902(4)
1.883(4)
Rh–P1
Rh–P3
P1–C4
P1–C11
P2–C18
P3–C20
P3–C22
Si–C2
2.2672(7)
2.3339(7)
1.840(3)
1.843(3)
1.840(3)
1.840(3)
1.827(3)
1.919(3)
1.519(4)
Rh–P2
Rh–Si
P1–C5
P2–C17
P2–C19
P3–C21
Si–C1
2.2823(7)
2.3937(8)
1.839(3)
1.832(3)
1.851(3)
1.841(3)
1.903(3)
1.906(3)
Si–C3
Si–C4
C3–C4
C1–C2
P1–Rh–P2
P1–Rh–Si
P2–Rh–Si
167.65(3)
81.24(3)
87.85(3)
P1–Rh–P3
P2–Rh–P3
P3–Rh–Si
95.96(3)
95.13(3)
176.58(2)
Cl–Rh–P1
Cl–Rh–P3
P1–Rh–P2
P1–Rh–Si
P2–Rh–Si
90.45(3)
92.31(4)
160.37(4)
85.10(4)
93.39(4)
Cl–Rh–P2
Cl–Rh–Si
P1–Rh–P3
P2–Rh–P3
P3–Rh–Si
88.20(4)
171.08(4)
102.52(3)
97.10(4)
96.20(4)
[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (2) (eqn. 2). Workup of the
resulting solution and recrystallization from toluene at Ϫ75 ЊC
gave orange crystals of 2 in 35% isolated yield. The structure of
2 has been determined by spectroscopic and analytical methods
and by X-ray crystal structure analysis.
(2)
The square planar complex 2 is fluxional in C6D5CD3 at
room temperature (Fig. 2). In the 1H NMR spectrum at
Ϫ40 ЊC, the two PMe3 ligands appear inequivalently at 0.80
and 1.32 ppm. When the temperature is raised, these signals
gradually broaden, coalesce, and finally become a slightly broad
signal at 1.08 ppm (20 ЊC). In the 31P{1H} NMR spectrum
at Ϫ40 ЊC, three sets of signals appear at Ϫ21.1, Ϫ9.0, and
70.5 ppm which are assigned to PMe3 trans to the silyl group,
PMe3 trans to PPh2, and PPh2, respectively. When the temper-
ature is raised, the two signals at Ϫ21.1 and Ϫ9.0 ppm assigned
to two PMe3 ligands gradually broaden, coalesce, and finally
become a broad triplet at 20 ЊC. At 20 ЊC, the signal of the
PPh2 moiety does not lose the coupling with two PMe3 ligands
and appears at 70.4 ppm as double triplets coupled with
103Rh (1J(RhP) = 160 Hz) and two 31P nuclei (2J(PP) = 131 Hz).
These spectroscopic features are consistent with the intra-
molecular exchange of two PMe3 ligands. Muetterties et al.
studied the dynamic behavior of Rh(CH2Ph)(PMe3)3 by
variable-temperature NMR spectroscopy.10 At 60 ЊC, the PMe3
resonances become equivalent and they lose their coupling with
the 103Rh nuclei. The observations are consistent with a flux-
ional process resulting from the intermolecular PMe3 exchange.
The reason for the difference in the exchange process of PMe3
ligands between the (2-phosphinoethyl)silyl complex 2 and the
benzyl complex is obscure at present. The 29Si resonance
appears at 42.3 ppm at 20 ЊC.
The ORTEP drawing of 2 is shown in Fig. 3. Selected bond
distances and angles of 2 are listed in Table 2. Complex 2 is
among a few coordinatively unsaturated silylrhodium() com-
plexes.4,5,11 The angles of P1–Rh–P2 and P3–Rh–Si are
167.65(3) and 176.58(2)Њ, respectively, indicating a slightly dis-
torted square planar coordination geometry of 2. The Rh–Si
bond length is 2.3937(8) Å which is relatively longer than those
of the previously reported coordinatively unsaturated silyl-
rhodium() complexes (Ph3Si)Rh(PMe3)3 (2.317(1) Å)5 and
(PhMe2Si)Rh(PMe3)3 (2.3804(10) Å).11a The change of the
Rh–Si bond lengths is ascribable to the degree of the M(dπ)–
SiX(σ*) interaction.12 When more electron-withdrawing groups
are bonded to silicon, this interaction becomes stronger and, as
a result, the Rh–Si bond becomes shorter. The silyl ligand in 2
bears three electron-releasing alkyl groups on the silicon atom
which make the Rh–Si bond of 2 the longest among them. In
Fig.
1
ORTEP drawing of RhH(Cl)[(κ2Si,P)-Me2Si(CH2)2PPh2]-
(PMe3)2 (1).
in accord with the above-mentioned characterization by NMR
spectroscopy. The Rh–H hydrogen atom was located by the
difference Fourier synthesis and refined isotropically. The bond
distance of Rh–H (1.71(8) Å) is reasonable compared with
those in previously reported hydridorhodium() complexes.
A strongly trans-influencing silyl group is located trans to
the weakly trans-influencing chlorine ligand. The Rh–Si
bond length (2.331(1) Å) lies in the normal range of
those in the previously reported electron-rich silylrhodium()
complexes.8 The bite angle of Si–Rh–P1 (85.10Њ) is character-
istic of those in the complexes containing five-membered
(2-phosphinoethyl)silyl chelate ligands.6
The reaction of RhCl(PMe3)3 with HSiPh3 was reported by
Osakada et al.8 The reaction proceeded at room temperature
to give mer-RhH(Cl)(SiPh3)(PMe3)3. The complex adopts a
geometry similar to 1 in which three phosphorus atoms are
mutually meridional and the silyl ligand is located at the
trans-position of the chlorine ligand. Importantly, in the reac-
tion of RhCl(PMe3)3 with HSiPh3, the oxidative addition of
Si–H is reversible, whereas in eqn. 1 the process takes place
irreversibly undoubtedly owing to the chelate effect of the
(2-phosphinoethyl)silyl ligand.
Synthesis of Rh[(ꢀ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (2)
It has been known that chloro(hydrido) complexes LnMCl(H)
reacted with a base such as an amine to give a coordinatively
unsaturated complex via elimination of HCl.9 We therefore
attempted the reaction of RhH(Cl)[(κ2Si,P)-Me2Si(CH2)2PPh2]-
(PMe3)2 (1) with NEt3 which was monitored spectroscopically.
However, no reaction was observed, even at 80 ЊC.
Treatment of 1 with 1 equiv. of MeLi in toluene at room
temperature resulted in nearly quantitative formation of
a coordinatively unsaturated silylrhodium() complex Rh-
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Fig. 2 Variable-temperature 1H (300 MHz, toluene-d8) and 31P{1H} NMR (121.5 MHz, toluene-d8) spectra of Rh[(κ2Si,P)-Me2Si(CH2)2PPh2]-
(PMe3)2 (2).
Liϩ[2]Ϫ releases a PMe3 molecule, which is then ligated by 2. It
is well known that the substitution reaction is accelerated in
the presence of reductant or oxidant via generation of 17 and
19-electron species.13
Synthesis of Rh[(ꢀ2Si,P)-Me2Si(CH2)2PPh2](PMe3)3 (3)
When the reaction of 1 with MeLi was performed in the
presence of PMe3, Rh[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)3 (3)
was formed in an almost quantitative yield (eqn. 3). Workup
(3)
and recrystallization from toluene at Ϫ75 ЊC gave orange crys-
tals of 3 (74% yield). The structure of 3 has been determined
using spectroscopic and elemental analysis data and by X-ray
crystal structure analysis. Complex 3 is much more stable than
the unsaturated complex 2.
A variable-temperature 31P NMR study of 3 suggests the
existence of a fluxional behavior of three PMe3 ligands. Three
broad signals are observed at Ϫ24.0, Ϫ13.9, and 65.8 ppm in
the 31P{1H} NMR at 20 ЊC. Cooling of the solution gives rise to
the sharpening of these signals, and at Ϫ30 ЊC, they become
three sharp multiplets coupled with 31P and 103Rh nuclei at
Ϫ22.8, Ϫ13.1, and 65.7 ppm, in an approximate intensity ratio
of 2 : 1 : 1. These can be assigned to two equatorial PMe3, one
axial PMe3, and PPh2, respectively. As the temperature is raised,
two multiplet signals at Ϫ24.0 and Ϫ13.9 ppm gradually
broaden and coalesce. At 60 ЊC, the signal of PPh2 loses the
coupling with three PMe3 ligands and appears as a broad
doublet (1J(RhP) = 158 Hz) at 66.8 ppm. The 31P resonance for
one axial and two equatorial PMe3 ligands appears as one
broad signal at Ϫ20.4 ppm. These coupling patterns of 31P
Fig. 3 ORTEP drawing of Rh[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (2).
good agreement with the strong trans-influence expected to the
silyl ligand in 2,2c the bond length of Rh–P3, which is trans to
the silyl ligand, is about 0.04 Å longer than those of Rh–P1 and
Rh–P2.
When the reaction of 1 with excess MeLi was carried out,
initial formation of 2 was confirmed spectroscopically. How-
ever, further reaction occurred to give the PMe3-adduct of 2
Rh[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)3 (3) in 30% isolated
yield. Although the formation mechanism of 3 by the reaction
of the intermediate 2 with MeLi is not clear, it would involve
generation of the anionic complex Liϩ[2]Ϫ resulting from the
electron-transfer reaction between 2 and MeLi. The anion
J. Chem. Soc., Dalton Trans., 2002, 2061–2068
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Table 3 Selected bond distances (Å) and angles (Њ) for Rh[(κ2Si,P)-
Me2Si(CH2)2PPh2](PMe3)3 (3)
resonances are consistent with the intermolecular exchange
process of three PMe3 ligands in the trigonal-bipyramidal
complex (eqn. 4).
Rh–P1
Rh–P3
Rh–Si
P1–C5
P2–C17
P2–C19
P3–C21
P4–C23
P4–C25
Si–C2
2.2836(9)
2.3099(9)
2.405(1)
1.850(4)
1.843(4)
1.835(4)
1.846(3)
1.838(4)
1.832(4)
1.906(4)
1.522(5)
Rh–P2
Rh–P4
P1–C4
P1–C11
P2–C18
P3–C20
P3–C22
P4–C24
Si–C1
2.3241(8)
2.3488(9)
1.853(4)
1.860(4)
1.853(4)
1.846(4)
1.844(4)
1.844(3)
1.913(4)
1.904(4)
(4)
Si–C3
The intermolecular exchange process of PMe3 ligands in
3 was also confirmed by a variable temperature 31P{1H}
NMR study on the mixture of 3 and PMe3 (Fig. 4). At 25 ЊC,
C3–C4
P1–Rh–P2
P1–Rh–P4
P2–Rh–P3
P2–Rh–Si
P3–Rh–Si
118.35(3)
91.32(3)
109.46(3)
91.50(3)
86.78(3)
P1–Rh–P3
P1–Rh–Si
P2–Rh–P4
P3–Rh–P4
P4–Rh–Si
130.51(3)
80.18(3)
99.45(3)
92.94(3)
168.45(3)
Fig. 5 ORTEP drawing of Rh[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)3 (3).
PMe3 ligand occupy the axial positions while the PPh2 moiety
and two PMe3 ligands are located in equatorial sites. The Rh–Si
bond length is 2.405(1) Å which is somewhat longer than that
of the previously reported silylrhodium() complex Rh(η4-Si-
(CH2CH2PPh2)3)(CO) (2.379(5) Å) in which the silicon atom
and a CO ligand are located in the axial positions.3 The length-
ening of the Rh–Si bond may be due to the stronger σ-donating
ability of the tertiary phosphine ligand compared to the CO
ligand.
Fig. 4 Variable temperature 31P{1H} NMR (121.5 MHz, toluene-d8)
spectrum of a mixture of Rh[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (3)
and PMe3 (* impurity).
four separate broad signals appear at 65.6, Ϫ14.5, Ϫ24.3, and
Ϫ56.8 ppm, assignable to PPh2, axial PMe3, equatorial PMe3,
and free PMe3, respectively. Cooling of the solution to Ϫ30 ЊC
gave four sharp signals at 65.7, Ϫ13.1, Ϫ22.8, and Ϫ56.8 ppm,
where the exchange of PMe3 is inhibited on the NMR time-
scale. When the temperature is raised, three broad signals of
PMe3 at Ϫ13.1, Ϫ22.8, and Ϫ56.7 ppm gradually broaden and
coalesce. At 80 ЊC, two separate resonances are present: one is a
In a previous paper, we reported the synthesis and properties
of iridium() and iridium() complexes having the (2-phos-
phinoethyl)silyl chelate ligand.16 The iridium analog of 1,
IrCl(H)[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)3 (1-Ir), was syn-
thesized by the thermal reaction of [Ir(CO)(PMe3)4]Cl with
HMe2Si(CH2)2PPh2 at 80 ЊC. The iridium complex 1-Ir has the
same geometry as the rhodium analog 1. The reaction of 1-Ir
with MeLi was carried out under conditions similar to those
described in eqn. 2. It afforded the iridium() complex
IrMe(H)[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)3, the rhodium()
analog of which was not detected in the reaction of 1 with
MeLi. Thermolysis of the iridium() complex in toluene at
55 ЊC led to elimination of methane to give the unidentified
product(s) with an Ir–H bond. No formation of Ir[(κ2Si,P)-
Me2Si(CH2)2PPh2](PMe3)2 (2-Ir) was observed. This striking
difference in the thermal stability between Rh and Ir complexes
is consistent with the general trend: The iridium complexes with
the metal center in high oxidation state  are more stable than
the corresponding rhodium complexes.18 When the thermal
reaction of 2-Ir was carried out in the presence of PMe3, a
coordinatively saturated silyliridium() complex Ir[(κ2Si,P)-
Me2Si(CH2)2PPh2](PMe3)3 (3-Ir) was formed, which adopts the
trigonal-bipyramidal geometry with the silyl and PMe3 groups
in the axial positions.
1
sharp doublet at 66.1 ppm (PPh2, J(RhP) = 160 Hz) without
the coupling with PMe3 and the other is a broad signal at Ϫ25.3
ppm (PMe3). These observations are also consistent with the
mechanism involving the intermolecular exchange of PMe3
ligands via formation of square-planar 2. The previously
reported Rh() silyl and methyl complexes of the type RhRL4
(R = Me,10 SiHPh2,14 L = PMe3) with a trigonal-bipyramidal
geometry also exhibit the intermolecular exchange of PMe3
15
ligands. In contrast, the iridium() complexes IrMe(PMe3)4
and Ir[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)3 exhibit the intra-
16
molecular exchange of PMe3 ligands on the NMR timescale.
These differences would be attributable to the strength of
metal–phosphorus bonds.17 In general, the iridium–phosphorus
bond is stronger than the rhodium–phosphorus bond.
The ORTEP drawing of 3 is shown in Fig. 5. Selected bond
distances and angles of 3 are listed in Table 3. The com-
plex 3 adopts a five-coordinate, slightly distorted trigonal-
bipyramidal structure in which the silyl silicon atom and a
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Reactions of Rh[(ꢀ2Si,P)-Me2Si(CH2)2PPh2](PMe3)n (n ؍ 2 (2),
3 (3)) with monohydrosilane
Complex 2 represents the first example of a coordinatively
unsaturated trialkylsilylrhodium() complex. Due to the strongly
electron-releasing character of the trialkylsilyl moiety, 2 is
expected to be highly reactive toward various small molecules.
In fact, the reaction of 2 with 6 equiv. of HSiMe2Ph proceeded
spontaneously at room temperature to give a hydrido(silyl)-
rhodium() complex 4 almost quantitatively, although isol-
ation of 4 was not successful due to its thermal instability
(eqn. 5). The presence of both Rh–H (δ Ϫ10.30, 1H) and Rh–
1
SiMe2Ph (δ 0.45, 6H) resonances in the H NMR spectrum at
Ϫ20 ЊC supports the structure shown in eqn. 5. The coupling
pattern of the 31P NMR spectrum established the geometry of 4
in which three phosphorus atoms are located at mutually fac-
positions. After 20 h at room temperature, the mixture of 4 and
HSiMe2Ph was converted to dihydrido complex RhH2[(κ2Si,P)-
Me2Si(CH2)2PPh2](PMe3)2 (5) and (SiMe2Ph)2 in 91% yield each
(eqn. 5). Characterization of (SiMe2Ph)2 was based on com-
Scheme 1
(5)
Fig. 6 Geometry of mer-[RhCl(H)(SiAr3)(PMe3)3].
tionally strong trans-effect of the silyl ligand in intermediate
4.20 Further reaction of 4 and mer-[RhCl(H)(SiAr3)(PMe3)3]
requires the dissociation of a PMe3 ligand, which allows it to
form bis(silyl)rhodium() intermediates. In complex 4, the
highly trans-effecting silyl moiety of (2-phosphinoethyl)silyl
chelate ligand would accelerate the dissociation of the trans-
PMe3 ligand, while such an effect is not operative in mer-
[RhCl(H)(SiAr3)(PMe3)3].
It has been known that the dehydrogenative coupling of
monohydrosilanes requires considerably severe conditions and
is accompanied by the scrambling of substituents on the silicon
atoms.21 It should be noted that the reaction (eqn. 5) proceeds at
room temperature to give the silicon–silicon coupling product
exclusively without the formation of the scrambling products.
parison of the 1H, 13C, and 29Si NMR spectra with the authentic
sample synthesized by the published procedure.22 The dihydrido
complex 5 was independently synthesized by treatment of 3
with H2 in 63% yield. It shows characteristic IR absorption
bands due to ν(Rh–H) vibrations at 1929 and 1884 cmϪ1. The
presence of two inequivalent hydrido ligands was confirmed by
1
the H NMR spectrum, which shows two hydrido peaks at δ
Ϫ10.57 and Ϫ9.27. The coupling pattern of two hydrido peaks
with three 31P and one 103Rh nuclei supports the geometry shown
in eqn. 5, which is confirmed by the 31P and 29Si NMR data.
Reaction of a coordinatively saturated silylrhodium() com-
plex Rh[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)3 (3) with HSiMe2Ph
was also examined. Treatment of 3 with 5 equiv. HSiMe2Ph in
C6D6 at room temperature afforded a mixture of 3, 4, and free
PMe3. After 89 h at room temperature, only a trace amount of
(SiMe2Ph)2 was formed and further reaction at 80 ЊC for 1 week
led to the decomposition of 3 and 4.
A plausible mechanism for the formation of 5 and (SiMe2-
Ph)2 is illustrated in Scheme 1. This mechanism firstly involves
the formation of 4 via oxidative addition of HSiMe2Ph. The
next step is the dissociation of PMe3 from 4 and then oxidative
addition of HSiMe2Ph takes place to give a silylrhodium()
intermediate RhH2(SiMe2Ph)2[(κ2Si,P)-Me2SiCH2CH2PPh2]-
(PMe3) (A). A silylrhodium() complex analogous to A has
been reported by Nagashima et al.19 Complex A undergoes
reductive elimination of (SiMe2Ph)2 and subsequent ligation of
PMe3 to Rh gives 5. In the reaction of 3 with HSiMe2Ph, the
resulting free PMe3 retards the further dissociation of a PMe3
ligand from 4.
As mentioned above, Osakada et al. reported the reaction of
RhCl(PMe3)3 with HSiAr3.8 The reaction proceeded at room
temperature to give the Si–H oxidative addition product mer-
[RhCl(H)(SiAr3)(PMe3)3] (Fig. 6). In this reaction, Si–Si reduc-
tive coupling products such as RhCl(H)2(PMe3)3 and (SiAr3)2
were not observed. Thus, the reaction in eqn. 5 is characteristic
of a coordinatively unsaturated silylrhodium() complex 2. The
dramatic difference in reactivity between 2 and RhCl(PMe3)3
is of great interest. This difference is attributable to the excep-
Conclusions
We have synthesized the novel silylrhodium() complexes
Rh[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (2) and Rh[(κ2Si,P)-
Me2Si(CH2)2PPh2](PMe3)3 (3). The structures of 2 and 3 were
determined by NMR spectroscopy and X-ray crystal structure
analysis. Complex 2 adopts a square-planar geometry and
exhibits the intramolecular exchange of PMe3 ligands. Complex
3 adopts a trigonal-bipyramidal geometry with the silyl moiety
and a PMe3 ligand occupying the axial positions. Complex 3
undergoes an intermolecular exchange process of PMe3 ligands
and generates the coordinatively unsaturated 2 under mild
conditions.
Dehydrogenative coupling of monohydrosilanes can be medi-
ated by the coordinatively unsaturated silylrhodium() complex
2. This novel reactivity seems to result from the strong trans-
effect character of silyl ligands. Introduction of (phosphino-
ethyl)silyl ligands would open up rich chemistry.
Experimental
General procedures
All manipulations were carried out under a dry nitrogen
atmosphere. Reagent-grade toluene and hexane were distilled
from sodium-benzophenone ketyl immediately before use.
J. Chem. Soc., Dalton Trans., 2002, 2061–2068
2065

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Benzene-d6 and toluene-d8 were dried over a potassium mirror
and transferred into an NMR tube under vacuum. HMe2-
Si(CH2)2PPh2 23 and [Rh(µ-Cl)(COD)]2 24 were prepared accord-
ing to literature methods. Other chemicals were purchased from
Wako Pure Chemical Industries, Ltd., and used as received. All
NMR data were recorded on a Bruker ARX-300 spectrometer.
29Si NMR spectra were obtained by the DEPT pulse sequence.
IR spectra were recorded on a Horiba FT-200 spectrometer.
the tube by syringe. The color of the solution immediately
changed from light yellow to orange. After 10 min, the color
of the solution became brown. The tube was attached to the
vacuum line again, and the reaction mixture was concentrated
to dryness and toluene (5 mL) was transferred into it. The tube
was flame-sealed and unsealed in an N2 glovebox. The reaction
mixture was filtered through a Celite pad. The filtrate was con-
centrated and cooled to Ϫ75 ЊC to allow the growing of orange
crystals which were collected by filtration to give Rh[(κ2Si,P)-
Me2Si(CH2)2PPh2](PMe3)3 (3) (98.4 mg, 0.163 mmol, 30%).
RhH(Cl)[(ꢀ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (1)
To a toluene solution (30 mL) of RhCl(PMe3)n (n = 3, 4),
prepared by refluxing the THF solution of [Rh(µ-Cl)(COD)]2
(699 mg, 1.42 mmol) (COD = 1,5-cyclooctadiene) and PMe3
(1.0 mL, d = 0.748 g cmϪ3, 9.80 mmol) for 14 h, was added
dropwise HSiMe2(CH2)2PPh2 (979 mg, 3.59 mmol). After add-
ition was complete, the mixture was stirred for 2 h at 50 ЊC.
Removal of volatiles under reduced pressure resulted in a pale
yellow oily residue, which was extracted with toluene (10 mL ×
3). The extract was filtered through a Celite pad and concen-
trated under reduced pressure. Recrystallization of the residue
from toluene–hexane at Ϫ10 ЊC gave ivory crystals of RhH(Cl)-
[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (1) (1.44 g, 2.56 mmol,
Rh[(ꢀ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (2)
Complex 1 (237 mg, 0.420 mmol) was placed in a Pyrex tube
(12 mm o.d.) having a Teflon needle valve at the top. The tube
was attached to a vacuum line, and toluene (5 mL) was trap-to-
trap-transferred into it. After the Teflon valve was closed, the
tube was detached from the vacuum line and attached to
an Argon line. An ether solution of MeLi (1.04 M, 0.45 mL,
0.47 mmol) was added into the tube by a syringe. The color of
the solution immediately changed from light yellow to orange.
The tube was attached to the vacuum line again and the reac-
tion mixture was stirred under high vacuum for 5 min. Volatiles
were removed and toluene (5 mL) was transferred into it. The
tube was flame-sealed and unsealed in an N2 glovebox. The
reaction mixture was filtered through a Celite pad. The filtrate
was concentrated to ca. 2 mL and cooled to Ϫ75 ЊC to allow the
growing of orange crystals which were collected by filtration
to give Rh[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (2) (77 mg,
1
90% based on Rh). H NMR (300 Hz, C6D6): δ Ϫ9.32 (dq,
2
1
2J(PtransH) = 158 Hz, J(PcisH) = J(RhH) = 15 Hz, 1H, RhH),
0.23 (s, 3H, SiMe), 0.38 (s, 3H, SiMe), 0.80 (d, 2J(PH) = 6.9 Hz,
9H, PMe3 (trans to RhH), 0.83 (m, 2H, SiCH2), 1.47 (dd,
3
2J(PH) = 8.9 Hz, J(PH) = 2.1 Hz, PMe3 (trans to PPh2), 2.08
(m, 2H, PCH2), 6.95–7.11 (m, 6H, m,p-Ph), 8.15, 8.30 (m, 2H ×
3
2, o-Ph). 13C{1H} NMR (75.5 MHz, C6D6): δ 6.7 (d, J(PC) =
1
0.146 mmol, 35%). H NMR (300 MHz, toluene-d8, 20 ЊC):
7.4 Hz, SiMe), 10.4 (d, 3J(PC) = 4.0 Hz, SiMe), 17.9 (dt,
1J(PC) = 20.2 Hz, 3J(PC) = 2.1 Hz, PMe3), 20.0 (ddd, 1J(PC) =
δ 0.58 (s, 6H, SiMe2), 0.70 (m, 2H, SiCH2), 1.08 (br., 18H, 2 ×
PMe3), 2.32 (m, 2H, PCH2), 7.02–7.09 (m, 6H, m,p-Ph), 7.86
(m, 4H, o-Ph). 1H NMR (300 MHz, toluene-d8, Ϫ40 ЊC): δ 0.80
3
28.7, J(PC) = 1.3, 3.6 Hz, PMe3), 20.7 (m, SiCH2), 27.9 (m,
PCH2), 127.9 (d, J(PC) = 10.0 Hz), 128.4 (d, J(PC) = 7.7 Hz),
129.5 (d, J(PC) = 8.8 Hz), 129.8 (d, J(PC) = 6.6 Hz), 132.2 (d,
2J(PC) = 8.9 Hz, o-Ph), 134.7 (d, 2J(PC) = 11.1 Hz, o-Ph), 138.0
(dt, 1J(PC) = 47.5 Hz, J(PC) = 7 Hz, ipso-Ph), 139.8 (dt, 1J(PC)
= 28.8 Hz, J(PC) = 4 Hz, ipso-Ph). 29Si{1H} NMR (59.6 MHz,
2
(d, J(PH) = 4.7 Hz, 9H, PMe3), 0.86 (s, 6H, SiMe2), 1.32 (d,
2J(PH) = 5.7 Hz, 9H, PMe3), 2.43 (m, 2H, PCH2), 6.95–7.07,
8.00 (m, 10H, PPh2). 13C{1H} NMR (75.5 MHz, C6D6, 20 ЊC):
δ 7.9 (s, SiMe2), 19.3 (m, SiCH2), 21.4–21.7 (m, 2 × PMe3), 35.2
(m, PCH2), 129.0, 129.3 (s, m,p-Ph), 134.1 (d, 2J(PC) = 13.0 Hz,
1
2
o-Ph), 140.3 (d, J(PC) = 24.6 Hz, ipso-Ph). 29Si{1H} NMR
C6D6): δ 40.4 (dddd, J(RhSi) = 26.1 Hz, J(PcisSi) = 10.5, 8.2,
6.9 Hz). 31P{1H} NMR (121.5 MHz, C6D6): δ Ϫ25.1 (broad m,
PMe3 (trans to RhH)), Ϫ7.6 (ddd, 2J(PPtrans) = 364 Hz, 1J(RhP)
1
(59.6 MHz, toluene-d8, 20 ЊC): δ 42.3 (m). 31P{1H} NMR (121.5
MHz, toluene-d8, 20 ЊC): δ Ϫ14.8 (br. t, 1J(RhP) = 130 Hz, 2 ×
2
= 108 Hz, J(PPcis) = 32 Hz, PMe3 (trans to PPh2)), 55.5 (ddd,
1
2
PMe3), 70.4 (dt, J(RhP) = 160 Hz, J(PP) = 131 Hz, PPh2).
31P{1H} NMR (121.5 MHz, toluene-d8, Ϫ40 ЊC): δ Ϫ21.1 (ddd,
2J(PPtrans) = 364 Hz, 1J(RhP) = 110 Hz, 2J(PPcis) = 26 Hz, PPh2).
IR (KBr pellet, ν/cmϪ1): 2900 (s), 1953 (vs, ν(RhH)), 1432 (s).
MS (70eV, DEI): m/z 562 (Mϩ, 19), 486 (Mϩ Ϫ PMe3, 100).
Anal. Calc. for C22H39Cl P3RhSi: C, 46.94; H, 6.98. Found: C,
47.21; H, 6.99.
2
1J(RhP) = 113 Hz, J(PPcis) = 35 Hz, PMe3 (trans to SiMe2,
Ϫ9.0 (ddd, 2J(PPtrans) = 296 Hz, 1J(RhP) = 148 Hz, 2J(PPcis) =
2
36 Hz, PMe3 (trans to PPh2)), 70.5 (ddd, J(PPtrans) = 296 Hz,
1J(RhP) = 157 Hz, 2J(PPcis) = 36 Hz, PPh2). Mass (70 eV, EI):
m/z 526 (Mϩ, 43), 450 (Mϩ Ϫ PMe3, 100), 374 (Mϩ Ϫ 2PMe3,
20). IR (KBr pellet, ν/cmϪ1): 1419 (m), 1298 (w), 1144 (w), 949
(s), 696 (m). Anal. Calc. for C22H38 P3RhSi: C, 50.19; H, 7.28.
Found: C, 49.77; H, 7.15.
Reaction of RhH(Cl)[(ꢀ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (1)
with an excess amount of MeLi
A Pyrex NMR tube (5 mm o.d.) was charged with 1 (34 mg,
0.061 mmol), benzene-d6 (0.7 mL) and MeLi (1.4 M ether solu-
tion, 0.1 mL, 0.14mmol). The NMR tube was connected to the
vacuum line and was flame-sealed. The reaction was monitored
Rh[(ꢀ2Si,P)-Me2Si(CH2)2PPh2](PMe3)3 (3)
1
Complex 1 (506 mg, 0.900 mmol) was placed in a round-
bottomed flask (30 mL) having a Teflon needle valve at the top.
The tube was attached to a vacuum line, and toluene (10 mL)
was trap-to-trap-transferred into it. After the Teflon valve was
closed, the tube was detached from the vacuum line and
attached to an argon line. An ether solution of MeLi (1.04 M,
0.96 mL, 0.998 mmol) and PMe3 (0.35 mL, 3.44 mmol) was
added into the tube by a syringe under an argon atmosphere.
The color of the solution immediately changed from light
yellow to orange. The tube was attached to the vacuum line
again, and the reaction mixture was stirred under high vacuum
for 10 min. The resulting solution was concentrated to dryness.
The tube was flame-sealed and unsealed in an N2 glovebox. The
residue was extracted with toluene (2 mL × 3) and the extract
was filtered through a Celite pad. The filtrate was concentrated
to ca. 2 mL and cooled to Ϫ75 ЊC to allow the growing of
by H and 31P NMR spectroscopy. The quick formation of
a coordinatively unsaturated Rh[(κ2Si,P)-Me2Si(CH2)2PPh2]-
(PMe3)2 (2) was observed. However, 2 finally disappeared and
the PMe3 adduct of 2 Rh[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)3(3)
was formed. The authentic syntheses and data of 2 and 3 are
described below.
Reaction of RhH(Cl)[(ꢀ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (1)
with an excess amount of MeLi
Complex 1 (306.7 mg, 0.545 mmol) was placed in a Pyrex tube
having a Teflon needle bulb at the top. The tube was attached to
a vacuum line, and toluene (5 mL) was trap-to-trap-transferred
into it. After the Teflon bulb was closed, the tube was detached
from the vacuum line and attached to the Argon line. An ether
solution of MeLi (1.14 M, 1.4 mL, 1.6 mmol) was added into
2066
J. Chem. Soc., Dalton Trans., 2002, 2061–2068

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Table 4 Crystallographic parameters of 1, 2, and 3
1
2
3
Formula
M
Crystal system
a/Å
b/Å
c/Å
α/Њ
β/Њ
C22H39SiP3ClRh
C22H38SiP3Rh
526.45
Triclinic
C25H47SiP4Rh
602.53
Orthorhombic
11.8518(3)
35.8507(8)
14.0432(2)
90
90
90
5966.9(4)
Pccn
8
562.92
Orthorhombic
15.1621(8)
25.695(1)
13.5872(6)
90
90
90
5293.5(4)
Pbca
8
11.4349(6)
12.9113(9)
9.5714(4)
100.379(5)
104.093(2)
106.562(3)
1265.5(1)
γ/Њ
V/Å3
¯
P1
2
Space group
Z
dcalc/g cmϪ3
Crystal size/mm
µ(Mo Kα)/cmϪ1
2θ max/Њ
1.413
0.20 × 0.20 × 0.05
9.78
1.381
0.20 × 0.20 × 0.10
9.16
55
1.341
0.10 × 0.10 × 0.10
8.38
55
55
T /K
150
22911
6018 (0.056)
257
150
150
23536
6620 (0.026)
280
No. of reflections measured
No. of unique data (Rint
No. of params
11725
5596 (0.047)
244
)
Residuals: R; Rw (all data)
Residuals; R1 (I > 2σ(I ))
No. of reflections to calc. R1
0.077; 0.215
0.048
5110
0.068; 0.189
0.037
5481
0.061; 0.119
0.035
4709
2
2
R = Σ(Fo2 Ϫ Fc2)/Σ Fo , Rw = [Σw(Fo2 Ϫ Fc2)2/Σw(Fo )2]1/2 R1 = Σ Fo| Ϫ |Fc /Σ|Fo| for I > 2.0σ(I ).
orange crystals which were collected by filtration to give Rh-
[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)3 (3) (402 mg, 0.667 mmol,
74%). H NMR (300 MHz, toluene-d8, 20 ЊC): δ 0.53 (s, 6H,
were solved by Patterson methods (PATTY) and refined by the
least-squares technique. All non-hydrogen atoms were located
and refined anisotropically. The coordinates of a hydrogen
atoms connected to Rh in 1 were determined by the difference
Fourier synthesis and refined isotropically. Other hydrogen
atoms were placed at their geometrically calculated positions.
Data reduction and refinement were performed using teXsan
software packages. Crystallographic data of 1, 2, and 3 are
listed in Table 4.
1
SiMe2), 0.67–1.07 (br., 29 H, SiCH2 and 3 × PMe3), 2.42
(m, 2H, PCH2), 7.05–7.13 (m, 6H, m,p-Ph), 7.66 (m, 4H, o-Ph).
2
1H NMR (300 MHz, toluene-d8, Ϫ30 ЊC): δ 0.65 (d, J(PH) =
5.3 Hz, 9H, PMe3 (axial)), 0.81 (s, 6H, SiMe2), 1.32 (s, 18H, 2 ×
PMe3 (equatorial)), 2.57 (m, 2H, PCH2), 6.99–7.16 (m, 6H,
m,p-Ph), 7.74 (m, 4H, o-Ph). 13C{1H} NMR (75.5 MHz,
toluene-d8, 20 ЊC): δ 10.2 (s, SiMe2), 23.0 (d, 2J(PC) = 42.9 Hz,
CCDC reference numbers 173810–173812.
See http://www.rsc.org/suppdata/dt/b2/b201208c/ for crystal-
lographic data in CIF or other electronic format.
1
SiCH2), 23.7–27.8 (br, 3 × PMe3), 35.9 (d, J(PC) = 27.6 Hz,
2
PCH2), 134.0 (d, J(PC) = 13.8 Hz, o-Ph), 144.9 (m, ipso-Ph).
31P{1H} NMR (121.5 MHz, toluene-d8, 20 ЊC): δ Ϫ24.0 (br.,
2 × PMe3), Ϫ13.9 (br., PMe3), 65.8 (br., PPh2). 31P{1H} NMR
(121.5 MHz, toluene-d8, Ϫ30 ЊC): δ Ϫ22.8 (ddd, 1J(RhP) =
154 Hz, 2J(PP) = 48, 116 Hz, 2 × PMe3 (equatorial)), Ϫ13.1 (dq,
Reaction of Rh[(ꢀ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (2) with
HSiMe2Ph
2
1J(RhP) = 95 Hz, J(PP) = 48 Hz, PMe3 (axial)), 65.7 (dtd,
A Pyrex NMR tube was charged with 2 (9 mg, 0.017 mmol),
HSiMe2Ph (15 µL, 0.098 mmol) and C6Me6 (1 mg, internal
standard), and benzene-d6 (0.7 mL) was introduced to this tube
under high vacuum by the trap-to-trap-transfer technique. This
tube was flame-sealed. The reaction was monitored by NMR
spectroscopy and proceeded spontaneously at room temper-
ature to give RhH(SiMe2Ph)[(κ2Si,P)-Me2Si(CH2)2PPh2]-
(PMe3)2 (4) quantitatively. When the reaction was continued at
room temperature for 20 h, the mixture of 4 and HSiMe2Ph
were converted to RhH2[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (5)
and (SiMe2Ph)2 in 91% yield each. Data of RhH(SiMe2Ph)-
2
2
1J(RhP) = 159 Hz, J(PP) = 116 Hz, J(PP) = 48 Hz, PPh2).
Mass (70 eV, DEI): m/z 526 (Mϩ Ϫ PMe3, 37), 450 (Mϩ
Ϫ
2PMe3, 100), 374 (Mϩ Ϫ 3PMe3, 22). IR (KBr pellet, ν/cmϪ1):
1432 (m), 1294 (w), 1151 (vw), 948 (s), 809 (m), 736 (m), 698
(m), 516 (m). Anal. Calc for C25H47 P4RhSi: C, 49.84; H, 7.86.
Found: C, 49.73; H, 7.62.
Variable temperature NMR of Rh[(ꢀ2Si,P)-
Me2Si(CH2)2PPh2](PMe3)3 (3) and PMe3
1
[(κ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (4): H NMR (300 MHz,
A Pyrex NMR tube (5 mm o.d.) was charged with 3 (14 mg,
0.0232 mmol) and PMe3 (5 µL, 0.0492 mmol), and toluene-d8
(0.6 mL) was introduced into this tube under high vacuum by
the trap-to-trap-transfer technique. The NMR tube was flame-
sealed. The dynamic behavior of PMe3 ligands was monitored
by 31P NMR spectroscopy.
toluene-d8, Ϫ20 ЊC): δ Ϫ10.30 (dq, 2J(PtransH) = 123 Hz,
2J(PcisH) = 1J(RhH) = 16 Hz, 1H, RhH), 0.45 (s, 6H, SiMe2Ph),
0.55 (m, 2H, SiCH2), 0.64, 0.68 (s, 3H × 2, CH2SiMe2), 0.76
2
2
(d, J(PH) = 5.9 Hz, 9H, PMe3), 0.90 (d, J(PH) = 6.5 Hz,
9H, PMe3), 2.00 (m, 2H, PCH2), 6.91, 7.55, 7.66 (m, Ph).
31P{1H} NMR (121.5 MHz, toluene-d8, 20 ЊC): δ Ϫ28.3
1
2
(ddd, J(RhP) = 80 Hz, J(PPcis) = 29, 32 Hz, PMe3), Ϫ18.2
(ddd, 1J(RhP) = 103 Hz, 2J(PPcis) = 25, 29 Hz, PMe3), 60.1 (ddd,
1J(RhP) = 82 Hz, 2J(PPcis) = 25, 32 Hz, PPh2).
X-Ray crystal structure determination of 1, 2, and 3
Intensity data for X-ray crystal structure analysis were collected
at 150 K on a Rigaku RAXIS-RAPID Imaging Plate diffract-
ometer with graphite-monochromated Mo Kα radiation. A
total of 44 images, corresponding to 220.0Њ oscillation angles,
were collected with 2 different goniometer settings. Exposure
time was 0.50 minutes per degree. Readout was performed in
the 0.100 mm pixel mode. For 1 and 2, numerical absorption
corrections were applied on each crystal shape. The structures
Rh[(ꢀ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (3) with HSiMe2Ph
A Pyrex NMR tube was charged with 3 (11 mg, 0.018 mmol),
HSiMe2Ph (15 µL, 0.098 mmol) and C6Me6 (1 mg, internal
standard), and benzene-d6 (0.7 mL) was introduced to this tube
under high vacuum by the trap-to-trap-transfer technique. This
J. Chem. Soc., Dalton Trans., 2002, 2061–2068
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tube was flame-sealed. The reaction was monitored by NMR
spectroscopy which confirmed the quick formation of the mix-
ture of 3, 4, and free PMe3. The prolonged reaction at room
temperature did not cause any change in the ratio of products.
In the course of the reaction, a trace amount of (SiMe2Ph)2 was
confirmed. Heating the resulting mixture at 80 ЊC gave rise to
decomposition of complexes 3 and 4.
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Synthesis of RhH2[(ꢀ2Si,P)-Me2Si(CH2)2PPh2](PMe3)2 (5)
H2 gas was bubbled through a toluene solution (3 mL) of 3 (60
mg, 0.010 mmol) at room temperature for 20 min. The color
gradually changed from orange to light yellow. Evaporation of
the resulting solution, followed by the addition of pentane
(0.5 mL) precipitated a light yellow solid. The solid was washed
by pentane (0.5 mL × 3) to give 5 (33 mg, 0.062 mmol, 63%) as a
light yellow powder. 1H NMR (300 MHz, toluene-d8) δ Ϫ10.57
2
2
1
(dq, J(PtransH) = 135 Hz, J(PcisH) = J(RhH) = 18 Hz, 1H,
2
2
1
RhH), Ϫ9.27 (dq, J(PtransH) = 135 Hz, J(PcisH) = J(RhH) =
21 Hz, 1H, RhH), 0.61, 0.83 (s, 3H, SiMe), 0.76–1.20 (m, 1H ×
2, SiCH2), 0.84 (d, 2J(PH) = 6.3 Hz, 9H, PMe3), 1.15 (d, 2J(PH)
= 6.0 Hz, 9H, PMe3), 1.82, 2.36 (m, 2H, PCH2), 6.95–7.14 (m,
6H, m,p-Ph), 7.48, 7.67 (m, 4H, o-Ph). 31P{1H} NMR (121.5
1
2
MHz, toluene-d8) δ Ϫ20.0 (ddd, J(PRh) = 88 Hz, J(PP) =
2
1
29 Hz, J(PP) = 19 Hz, PMe3), Ϫ11.3 (dt, J(PRh) = 101 Hz,
2J(PP) = 27 Hz, PMe3), 68.2 (dt, J(PRh) = 101.1 Hz, J(PP) =
22 Hz, PPh2). Mass (70 eV, DEI): m/z 526 (Mϩ-2H, 100), 450
(Mϩ-2H–PMe3, 44). IR (KBr pellet, ν/cmϪ1): 2362 (s), 2337 (s),
1926, 1884 (s, ν(RhH)), 939 (s). Anal. Calc. for C22H40SiP3Rh:
C, 50.00; H, 7.63%. Found: C, 49.29; H, 7.44%.
1
2
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Acknowledgements
This work was supported by Grants-in-Aid for Scientific
Research (Nos. 11740367, 12640533, and 13029012) from
the Ministry of Education, Culture, Sports, Science and
Technology, Japan and financial support from the Nissan
Science Foundation, Inoue Foundation for Science, and
Tokuyama Science Foundation. We thank Shin-Etsu Chemical
Co., Ltd., and Toray Dow Corning Silicone Co., Ltd., for their
gifts of silicon compounds.
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